Compound type transmissions have been used advantageously for many years in heavy duty truck applications where a large number of transmission change gear ratios are employed in a manner to provide an efficient and smooth shifting performance over the speed range of the truck considering inertia and load factors involved.
Compound transmissions generally feature a combination of a main transmission section coupled in series with an auxiliary transmission section such that the number of forward change gear ratios obtainable from the combination is the product of the number of gear ratios respectively contained within the main and auxiliary transmission sections as is well known to those skilled in the art. Thus, for example, the number of gear ratios is sixteen for a compound transmission in which four gear ratios are contained within each of the main and auxiliary transmission sections coupled together in series.
The availability of particular gear ratios from the combination of the main and auxiliary sections of a compound type transmission have been the subject of considerable investigation in the past.
Broadly, compound transmissions are operative to provide a plurality of groups containing a plurality of forward gear ratios ranging from a first group that includes the lowest gear ratio to a last or highest group that includes the highest gear ratio available from the compound transmission.
More particularly, either range type or splitter type auxiliary sections or combinations of the the two have been employed to provide particular gear shifting sequence patterns. In compound transmissions having a range type auxiliary section, the auxiliary gear ratio steps are greater than the total ratio coverage of the main transmission section and the main transmission section is shifted progressively through its ratios in each range. Examples of compound transmissions having a range type auxiliary section can be found in U.S. Pat. Nos. 2,637,221; 2,637,222; and 3,105,395, the disclosures of all of which are included herein by reference.
In compound transmissions having a splitter type auxiliary section, the ratio steps of the splitter auxiliary section are less than the ratio step of the main transmission section and each main section ratio is split, or subdivided, by the splitter section. Examples of compound change gear transmissions having splitter type auxiliary sections may be seen by reference to U.S. Pat. Nos. 3,799,002; 4,290,515; 4,440,037; and 4,527,447, the disclosures of all of which are to be included herein by reference.
In a combined range and splitter type auxiliary section, both range and splitter type ratios are provided allowing the main section to be progressively shifted through its ratio in at least two ranges and also allowing the main section ratios to be split in at least one range. Examples of combined range and splitter auxiliary transmissions sections may be seen by reference to U.S. Pat. Nos. 3,283,613 and 3,648,546, the disclosures of which are respectively included herein by reference.
Until the recent past, compound transmissions, particularly for trucks, have historically been of the manual type requiring actuation of a clutch by an operator to shift between change gear ratios. Due to the large number of change gear ratios normally associated with compound transmissions, a great deal of effort was required to manually shift throughout the entire change gear ratios involved. More recently, efforts have been employed to combine manual shifting and automatic shifting under certain conditions such as disclosed in U.S. Pat. Nos. 4,208,929; 4,294,341; 4,312,248; and 4,324,153, the disclosures of all of which are included herein by reference.
Although a great deal of effort has been expended in the recent past to reduce operator fatigue and improve fuel economy, no one prior to the present invention had thought to provide standard or compound type transmissions with a shift control system that enabled manual shifting of lower gear ratios whilst enabling automatic shifting between particularly sequentially related higher gear ratios to relieve the operator of shifting burden under higher speed highway driving conditions and allow an automatic shift schedule for fuel economy.